Enhanced adsorption of fluoride from aqueous solutions by hierarchically structured Mg-Al LDHs/Al2O3 composites

Hierarchically structured layered double hydroxides (LDHs)/Al 2 O 3 composites were fabricated from waste paper fibers using a two-step method. In the first step microscaled Al 2 O 3 fibers were prepared by template-directed synthesis employing waste paper fibers as templates; and in the second step nanoscaled LDHs platelets were fabricated into hierarchical architectures based on crystal growth on Al 2 O 3 fibers surface. The morphology and structure of asprepared samples were characterized by scanning electron microscopy (SEM), N 2 adsorption/desorption analysis and X-ray diffraction (XRD) analysis. The SEM results revealed that the inorganic fibers were covered by LDHs platelets, forming the hierarchical structures with micro- to nanoscales. The BET analysis showed that the surface area was increased from 76.66m 2 /g (Al 2 O 3 fibers) to 165.0m 2 /g (composites) by the growth of LDHs platelets on the surfaces of Al 2 O 3 fibers. As compared to bare LDHs particles and Al 2 O 3 fibers, the LDHs/Al 2 O 3 composites show a high fluoride adsorption capacity, and the maximum adsorption capacity can reach up to 58.7mg/g. The Langmuir isotherm model was found to agree well with the equilibrium data, while the pseudo-second order model provided the highest correlation of the kinetic data for fluoride adsorption. The as-prepared LDHs/Al 2 O 3 composites and corresponding design strategies developed herein are expected to be applicable to the synthesis of other LDHs based composites for the removal of pollutants from water.